This invention pertains to a process of hydrogenating aliphatic dialdehydes, preferably alicyclic dialdehydes, with hydrogen in the presence of a hydrogenation catalyst to prepare the corresponding aliphatic diols, preferably, alicyclic diols.
Aliphatic diols find utility as solvents and as intermediates in the preparation of industrially useful chemicals. Alicyclic diols, such as the cis/trans isomers of 1,3- and 1,4-cyclohexanediol, are known to be useful as solvents and as intermediates in the manufacture of plasticizers and detergents.
It is known that aldehydes can be catalytically reduced with hydrogen in the presence of a hydrogenation catalyst to form alcohols. Hydrogenation catalysts advantageously comprise at least one metal of Groups 6, 7, 8, 9, 10, 11, or 12 of the Periodic Table of the Elements, referenced as described hereinafter. The hydrogenation of aldehydes can be carried out continuously or batchwise in a gas or liquid phase. For the industrial production of alcohols via the hydrogenation of aldehydes obtained from hydroformylation of olefins (“OXO process”), preference is given to continuous gas or liquid phase processes using hydrogenation catalysts in a fixed bed. As used herein, the term “hydroformylation” refers to a process of contacting an olefinically-unsaturated compound characterized by at least one unsaturated carbon-carbon (C═C) double bond with carbon monoxide and hydrogen (synthesis gas or syngas) in the presence of a hydroformylation catalyst to obtain therefrom an aldehyde product characterized by a carboxaldehyde (formyl) substituent (—CH═O). Hydroformylation catalysts comprise a transition metal complexed to an organophosphorus ligand, advantageously, an organophosphite ligand, and preferably, a triorganomonophosphite or an organobisphosphite ligand.
High molecular weight aldehydes, that is, aldehydes having 6 or more carbon atoms (C6+), are preferably hydrogenated in the liquid phase, particularly, as the molecular mass and boiling point of such compounds are generally too high for a gas phase process. Hydrogenation in the liquid phase presents a disadvantage, however, in that owing to high concentrations of both aldehydes and alcohols the formation of high boilers is promoted via secondary reactions. In particular, aldehydes can undergo aldol reactions (addition and/or condensation) with alcohols to form unsaturated aldehydes (enals), hemiacetals and/or acetals. The hemiacetals and acetals can subsequently undergo elimination of water or alcohol, respectively, to form enol ethers, which under hydrogenation conditions form saturated ethers. Dialdehydes can undergo self-condensation to produce heavies, including dimers, trimers, and higher oligomers. All of the enal, hemiacetal, acetal, enol ether, and saturated ether by-products as well as self-condensation heavies are considered “heavies” and they reduce the yield of the desired alcohol.
The hydrogenation of high molecular weight aldehydes having 6 or more carbon atoms prepared via hydroformylation presents additional problems in liquid phase hydrogenation of the aldehydes to alcohols. Due to the high molecular weight of C6+ aldehyde products, the viscosity of such aldehydes can be unacceptably high, which consequentially increases difficulties in transporting and handling these aldehydes in a liquid phase. Moreover, hot spots might develop in an unacceptably viscous liquid phase leading to an increased production of heavies. Additionally, the aldehyde feed to the hydrogenation process, being obtainable from a hydroformylation process, disadvantageously can contain a low quantity of one or more organophosphite ligands and/or degradation products derived from the organophosphite ligand(s). These organophosphites or their degradation products are capable of binding and poisoning the hydrogenation catalyst. As a further disadvantage, the hydrogenation of di- and poly-carboxaldehydes generally results in increased formation of polymeric heavies (including dimers and trimers) and lactones, as compared with the hydrogenation of mono-carboxaldehydes. In addition, di- and poly-carboxyaldehydes can engage in intramolecular side reactions to form, for example, cyclic acetals and lactones.
In view of the above, an improvement in the liquid phase hydrogenation of aliphatic dialdehydes, preferably C6+ alicyclic dialdehydes derived from hydroformylation processes, is desirable in preparing the corresponding diols, preferably, C6+ alicyclic diols.
U.S. 2007/0161829 A1 discloses use of a controlled amount of water in a hydrogenation stage of an oxo product for the production of alcohols, which uses at least two reactors in series with a reduction in the amount of sulfur, chlorine and hydroformylation catalyst residues fed to the hydrogenator. A quantity of water from 0.5 to 3 weight percent, especially from 1 to 2 weight percent, is used based on the weight of the product injected into the hydrogenator.
U.S. Pat. No. 6,680,414B2 discloses a process of hydrogenating an aldehyde product derived from the hydroformylation of one or more C4-C16olefins, such as dibutene. The hydrogenation is conducted in the presence of an excess of hydrogen, a Group 8 transition metal catalyst, and from 0.05 to 10 percent by weight of water so as not to form a separate aqueous phase.
U.S. Pat. No. 5,059,710 and U.S. Pat. No. 4,401,834 disclose pretreating a hydroformylation aldehyde product with water in a thermal treatment zone prior to hydrogenation. It is disclosed that water may be added to the hydrogenation in an amount from about 1 to 8 volume percent, based on the volume of aldehyde feed.
U.S. Pat. No. 2,809,220 discloses a vapor phase hydrogenation of aldehydes in the presence of hydrogen, a sulfurized hydrogenation catalyst, and added water vapor. The amount of water introduced into the hydrogenation zone is preferably from 1 to 10 moles water per mole acetal, or preferably from about 1 to 8 volume percent, based on the volume of aldehyde feed. In order to maintain the added water in a vapor phase, a large excess of hydrogen is employed (e.g., liquid feed rate from 0.25 to 2 v/v/h and hydrogen feed rate 5000-20,000 ft3/barrel of feed)